Solid Substrate Formulations of the Mycoherbicide Colletotrichum truncatum for Hemp Sesbania (Sesbania exaltata) Control

Colletotrichum truncatum was grown on kernels of eight different grains for 3 or 4 weeks at room temperature (22-24°C). Fresh preparations of conidia as well as fungus-infested corn and rice suspensions resulted in 100% mortality of hemp sesbania seedlings when sprayed postemergence with a 14 h dew period. Fresh preparations of mycelia and fungus-infested sorghum suspensions resulted in 90 and 65% mortality of hemp sesbania seedlings, respectively. Lower mortality (≤15%) occurred with the other ground fungus-infested grain suspensions. Fresh preparations of conidia, fungus-infested corn, rice and sorghum, and mycelia, when applied to soil pre-emergence, resulted in 100, 94, 100, 83 and 71% mortality of hemp sesbania seedlings 14 days after application, respectively. Lower mortality (≤23%) occurred with the other ground fungus-infested grain preparations. Freshly-prepared C. truncatum at 6.25, 12.5, 25 and 50 mg fungus-formulated rice cm^-2 of soil surface, applied pre-emergence or at the time of planting, killed 97, 100, 100 and 100% of hemp sesbania, respectively. After storage at 22-24°C for 6 to 24 months, the rice formulation caused 67 to 93% mortality after 6 months, 39 to 81% after 12 months, and ≤2% after 24 months, respectively. When C. truncatum was refrigerated at 4-6°C, the rice formulation retained good efficacy through 24 months, and when frozen, for up to 8 years. C. truncatum formulated on rice stored under all the above conditions contained mainly sclerotia at 2.4 x 10⁵ sclerotia g^-1. C. truncatum killed hemp sesbania seedlings with a single soil application through 4 plantings on the same soil. These results indicate that rice and possibly corn are excellent solid substrates for the formulation of C. truncatum. This is a simple and effective method for enhancing the activity of C. truncatum against hemp sesbania.